On Oct. 25, 1999, about 1213 central daylight time (CDT), a Learjet Model 35, N47BA, operated by Sunjet Aviation, Inc., of Sanford, Fla., crashed near Aberdeen, S. Dak. The airplane departed Orlando, Fla., for Dallas, Tex., about 0920 eastern daylight time (EDT). Radio contact with the flight was lost north of Gainesville, Fla., after air traffic control cleared the airplane to flight level 390. Several U.S. Air Force and Air National Guard aircraft intercepted the airplane as it proceeded northwest-bound.
The military pilots in a position to observe the accident airplane at close range stated (in interviews or via radio transmissions) that the forward windshields of the Learjet seemed to be frosted or covered with condensation. The military pilots could not see into the cabin. They did not observe any structural anomaly or other unusual condition. The military pilots observed the airplane depart controlled flight and spiral to the ground, impacting an open field. All occupants on board the airplane, the captain, first officer, and four passengers, were killed, and the airplane was destroyed. The National Transportation Safety Board determined the probable cause of this accident was incapacitation of the flight crewmembers because of their failure to receive supplemental oxygen following a loss of cabin pressurization, for undetermined reasons.
The airplane included an oxygen system that provided emergency oxygen for the flight crew and passengers comprising of a single oxygen bottle, an oxygen bottle pressure regulator with a shutoff valve, an oxygen pressure gauge, an overboard discharge relief valve and indicator, flight crew mask quick disconnect valves, flight crew masks, a manual passenger shutoff valve, an oxygen aneroid valve, an oxygen aneroid bypass shutoff valve, passenger oxygen actuator lanyard valves, and passenger masks. Oxygen was available to the flight crew at all times during the flight when the oxygen bottle pressure regulator shutoff valve is open, as it was at the time of impact.
If the pilots had received supplemental oxygen from the airplane's emergency oxygen system, they likely would have properly responded to the depressurization by descending the airplane to a safe altitude. Therefore, it appears that the partial pressure of oxygen in the cabin after the depressurization was insufficient for the flight crew to maintain consciousness and that the flight crewmembers did not receive any, or adequate, supplemental oxygen.
What is needed then, is a system, method, and apparatus for supplying a locally oxygen-rich environment during depressurization allowing flight crewmembers sufficient time to respond and to take corrective measures including the donning of an oxygen mask.